1. Field of the Invention
The present invention is directed generally to a process and apparatus for electrically stunning poultry, and more specifically, to an apparatus incorporating a microprocessor based, current regulated output electrical circuit for the precise, individually controlled electronic stunning of poultry.
2. Description of the Background of the Invention
Poultry production has been a rapidly growing industry over the last twenty years. In the United States, it has been estimated that broiler chicken liveweight production was over 550 million pounds per week in 1992 while annual turkey liveweight production exceeded 6 billion pounds in 1990. It is further estimated that the national average of broiler undergrades in 1988 was approximately forty-six percent, translating to losses to the industry of hundreds of millions dollars for that year alone. Thus, even in such a mature industry, there is significant room for technological advances which improve the quality of the process. While the invention described herein has applications in other livestock processing, including hog processing, by way of example only, the present invention and the description of the background thereof will be described as it relates to the poultry industry.
During production, several factors contribute to the downgrading of the poultry. Such factors include the breed and strain of the poultry, the environment and management of the operation, nutrition, live handling, and processing, with the majority of downgrades caused by live handling, including live receiving and hanging of the birds, and the subsequent processing.
In the live handling and processing of poultry, it is a generally accepted practice in the industry that the animals be rendered unconscious by an electric current (electronarcosis) prior to slaughter. The stunning process relaxes the animals as they enter the slaughter mechanism. The slaughter mechanism typically comprises a form of mechanical knife that slits the blood vessels in the neck. Thereafter, the animals require a certain bleed out time during which they expire due to blood loss.
In a conventional processing line, the animals are initially hung on metal shackles by their feet. Those shackles are connected to each other, forming a conveyor line along a horizontal track which moves the poultry through the processing plant. The shackles and associated conveyor hardware are typically constructed of a conductive material and tied to an electrical ground. Thus, the shackles serve the additional purpose of providing an electrical ground during the stunning process. The heads, and optionally, the shoulders of the poultry are passed through a bath of a conductive liquid which is electrically charged. Once in the bath, the animals complete the circuit, providing a path for the current to pass from the charged bath to ground potential, such path preferably passing through the animal's brain.
The ability to obtain a consistent stun is critical to the processing of poultry. If the stun is too harsh, blood vessels may burst, causing unsightly hemorrhaging or causing bones to shatter. Further, the electric stun may actually kill the bird which may affect the amount of total bleed out. If the stun is too light, the animal may revive early in the kill or bleed out cycle and the violent thrashing pursuant to such revival may cause similar damage and hemorrhaging in the wing tips. In each case, expensive hand carving is required and the meat must be downgraded. It is estimated that upwards of ten percent of the birds sustain some form of stun damage.
Previous research has focused on certain parameters of the stun process. For example, with respect to the bath, saline concentration at one percent is generally considered to be optimum. However, water has been shown to be effective as well. Further, it is critical that the animals remain in contact with the bath. To achieve better contact, rub bars have been developed which prevent an animal from lifting up when it feels the charge. U.S. Pat. No. 4,751,767 to Walther is directed to a bubbler which lifts the level of the saline solution in the vicinity of each animal's head to provide better contact. The use of a foot fogger to dampen the animals feet to provide better contact has been recommended.
The teachings of the art vary with respect to the optimum charge which should be applied. Some 60 Hz AC systems are believed to be too harsh on the birds. Typically, a 400 Hz, 115 V, 11-50 ma AC signal, or alternatively, a 1000 Hz pulsed DC signal, may be used. A major manufacturer of stunning equipment, in its technical literature, indicates that stunning is a function of power and time and recommends a type of trial and error procedure to set the proper charge, indicating that most processing plants can operate its stunner at 20-25 V DC with 200-400 ma applied to the bath containing multiple birds. The one common factor in the industry is that the stunning charge is applied using a constant voltage source. Therein lies a major problem with the state of the art for it is widely believed that it is the amperage (current) which induces unconsciousness in the birds during stunning and it is the voltage which provides the pressure to push the current through the bird.
In a typical broiler processing plant, the birds are stunned for seven to ten seconds, with fourteen to twenty birds in the bath at any one time. With the shackles only six inches apart, a new entry into the bath or an exit from the bath occurs every half second. Additionally, as will be further detailed herein, the impedance/resistance of a bird varies from bird to bird and, in fact, varies over time during the stun cycle.
To describe that process in electrical terms, a parallel electrical circuit is formed with up to twenty individual resistors present, each with varying resistive values, at any one time. Depending on the quantity and particular mix of birds ("resistors") in the bath at any one time, the stunning current applied to each bird varies significantly. This results in some individual birds being understunned while others are overstunned, causing extensive damage as described above. Further, should the bath contain fewer than the typical fourteen to twenty birds, the birds that are in the bath will be severely overstunned.
Cardiac arrest stunning differs from the electronarcosis described above in that the poultry is killed by the electrical circuit rather than such poultry merely being stunned. In a 1989 paper on cardiac arrest stunning, Grandin recommends the use of a constant current power source to induce cardiac arrest. While Grandin recognizes that the resistance from bird to bird may differ, she does not teach of the varying resistance of each bird over time during the stunning cycle. Further, Grandin does not solve the parallel circuit electrical problem identified above, recommending instead that a large total current be supplied such that the average current per bird after the total current is divided across the parallel circuit should be sufficient for inducing cardiac arrest.
With respect to other problems in the prior art, electrical malfunctions of any of the commercial processing systems may cause either inefficient operation or result in expensive down time while repairs are performed. It is further noted that none of the current systems have a reliable self-test capability and an automatic "hot" spare back-up stunning circuit available therein.
Thus, the need exists for a stunning apparatus which overcomes those and other problems associated with the present systems which improves both productivity and quality. Such a stunning apparatus should be capable of delivering a current regulated output signal sufficient to effectively stun each bird during the entire stun cycle, regardless of the number of birds being processed at the time. Further, the need exists for a stunning apparatus which may adopt its regulated current output to the particular profile of the bird being processed. Still further, the need exists for such an apparatus to have a real-time self-test and fault tolerance capability. The apparatus must be modular and adaptable to processing lines already in use to avoid extensive and expensive rework of such lines. Finally, the apparatus must minimize the amount of moving parts in a slaughter house to facilitate maintenance and reliability.